Cache half-pixel interpolated reference frames, to avoid duplicate motion compensation.
30-50% speedup at subq=5. Patch by Radek Czyz. git-svn-id: svn://svn.videolan.org/x264/trunk@123 df754926-b1dd-0310-bc7b-ec298dee348c
30-50% speedup at subq=5. Patch by Radek Czyz. git-svn-id: svn://svn.videolan.org/x264/trunk@123 df754926-b1dd-0310-bc7b-ec298dee348c